1. Field of the Invention
The present invention relates to a seat reclining mechanism for automobiles and more particularly to a seat reclining mechanism having a reduction gear mechanism.
2. Description of Prior Art
Japanese Utility Model publication No. 58-1255 discloses a seat reclining mechanism having a reduction gear mechanism. The seat reclining mechanism is particularly applicable to a vehicle seat, especially to a passanger car seat and includes an upper bracket adapted to be secured to the seat back of a seat assembly and a lower bracket adapted to be secured to the seat cushion. Between the upper and lower brackets, there is provided a reduction gear mechanism through which the inclination angle of the upper bracket is adjusted. The reduction gear mechanism is comprised of an internal gear provided on the upper bracket and an external gear provided on the lower bracket and having gear teeth which are smaller in number at least by one than gear teeth in the internal gear. There is provided an eccentric shaft which carries the internal and external gears in an eccentric relationship so that the external gear is engaged with the internal gear at a circumferential position. A rotation of the eccentric shaft causes a displacement of the circumferential position of the engagement between the internal and external gears to thereby produce a relative rotation of the internal gear with respect to the external gear. This will cause a change in the inclination angle of the upper bracket with respect to the lower bracket.
In the seat reclining mechanism proposed by the Japanese utility model, the reduction gear mechanism has a large reduction gear ratio so that the position of the upper bracket can be maintained mostly by the friction between the eccentric shaft and the gears. It will therefore be understood that there is a substantial amount of friction between the eccentric shaft and the gears and a substantial actuating force is required to rotate the eccentric shaft.